The use of filter dyes in photographic elements for the absorption of unwanted radiation is known.
Filter dyes may be located in several locations in an element. They may be in a radiation-sensitive layer, an overcoat layer, in a layer adjacent to the radiation-sensitive layer, in an interlayer in a multilayer element, in an undercoat layer adjacent to the support or in a backing layer on the side of the support opposite the radiation-sensitive layer.
When incorporated directly in the radiation-sensitive layer they can function to improve sharpness by absorbing light scattered from one silver halide grain to another. Such dyes are referred to as absorber dyes. Absorber dyes also function to retard the sensitivity of one light sensitive layer relative to another in a multilayer element. By absorbing some of the exposing radiation the filter dye aids in balancing the sensitivities of all the light sensitive layers. A particular problem often associated with absorber dyes is the desorption of spectral sensitizing dyes from the grain surface. This is referred to an unsensitization.
Absorber dyes used in the red sensitive layer are often called cyan absorber dyes (cyan colored dyes which absorb red light). A currently used absorber dye in the red sensitive layer of a multilayer color photographic element is the anthraquinone dye "Sulfomethyl Blue". While this dye is very soluble and wahses out very rapdily during photographic processing, its use results in the buildup of sludge in the processing solutions, which is a particular disadvantage in high volume processors.
Filter dyes that function primarily to absorb unwated radiation due to reflection or refraction from layer interfaces, the layer-support interface, and particularly from the back side of the support, are referred to as antihalation dyes. The layers that contain them are referred to as antihalation layers.
The choice of filter dyes or other radiation absorbing compounds and their location in an element depend on a number of factors. A suitable dye must satisfy several requirements. The dye must of course absorb light in the desired spectral region. Frequently, it is also important that the dye not absorb radiation in other spectral regions. To be incorporated in an element, it is sometimes important that the dye be water soluble. It is usually important that the dye not migrate from the layer in which it is incorporated during or after coating. It preferably should not have adverse effects on the light sensitive layer. This is particularly important for an absorber dye. It is almost always important that the dye be easily and completely bleached or otherwise removed from the element during processing, and not be regenerated. This last requirement is important since residual dye in the coating is a source of objectionable stain.
Dye stain continues to be a problem associated with filter dyes. This problem is exacerbated by trends in the photographic industry to systems with very short processing times. Shortened processing times in, for example, x-ray and microfilm processing systems, necessitate shortened wash times, which mean less time for dye removal.
It is an objective of this invention to provide filter dyes for photographic elements which meet the foregoing requirements for filter dyes and that also do not cause post process dye stain or sludge.